As disclosed in U.S. Pat. No. 3,945,770 of the present inventor, sample collection apparatus utilizing a collection head has been devised. The sample collection apparatus is particularly valuable in obtaining a small sample for analytical purposes. Sometimes, it is very difficult to get a small sample out of a large flow. This difficulty finds analogy in attempting to draw a thimble full of water from a fire hydrant. When it is turned on, it is almost impossible to get only a thimble full. The apparatus of the referenced patent provides a means whereby small samples can be obtained from any size flow in a pipeline or other vessel.
This is equipment which is intended to be installed and left indefinitely to operate for months without significant service. The present disclosure is directed to improvements in that apparatus. These improvements particularly assist in extending the life of the equipment. In larger diameter sample collection heads which must be used to collect larger samples, there is real risk of material fatigue in the collection head which destroys the effectiveness of the equipment after prolonged operation. The life of the equipment is thereby limited, depending on the rate of operation and other scale factors. As has been discovered in the perfecting of the disclosed apparatus, there is a tendency for the sample collection head to form a high vacuum as it works against an opposing face formed of non yielding material. The formation of vacuum on the exposed face of the sample collection head forms tensile stress in the collection head. This tensile stress eventually will strain the collection head and perhaps permanently damage it. This deformation can take several forms. In one form, the deformation is first found at the bond between the push rod and the sample collection head. This bond typically will tear or break. The resilient plug tears along a line determined by the overhanging lip locking over the end of the plug. This situs of failure is geometrically determined.
The present apparatus is an improvement which incorporates a means securing the collection head. Thus, when the push rod forces the collection head against the opposing face, the dished area disappears as the collection head resiliently yields against this force. A natural restoring force in this resilient material is created as the push rod is retracted. In light of the fact that the sample collection head is not normally bonded to a washer and is captured slidably within a surrounding cylindrical shield, an internal restoring force normally does restore the collection head to its intended and original shape. However, the stress and consequential bond rupture which occurs as described above will interfere with this operation after continued use depending on a number of scale factors. The scale factors involved include the type of rubber, the dimensions of the collection head, the depth of the indention formed in the head, and many other factors. It is sufficient to note that the apparatus disclosed herein markedly improves the performance of the sample collection head. Accordingly, this apparatus is an improved sample gathering apparatus wherein the improvement incorporates a projecting mounting post which extends into the body of the resilient material which forms the collection head. The resilient material is shaped into a plug and has a dished exposed face. The mounting post is undercut to define a grasping shoulder where, at the time of fabrication, the plug is held on the push rod.